Pole in American airspace (5)

I believe the answer is:

sinus

'airspace' is the definition.
(I've seen this before)

'pole in american' is the wordplay.
'pole' becomes 's' (abbreviation for South, as in South Pole).
'american' becomes 'US' (United States).
's'+'in'+'us'='SINUS'

(Other definitions for sinus that I've seen before include "Air-filled cavity in one's head" , "Cavity within a bone" , "Passage in the head" , "Space in temple" , "Head space" .)

I've seen this clue in The Sun.

Want a hint initially instead of a full solution? Install my app